1. Field of the Invention.
The present invention relates to an activity sensing pacemaker which senses activity or motion along several different axes, such as the X axis, the Y axis and the Z axis, utilizing an array of motion sensors or acceleratometers and to pulse generating circuitry for controlling the output of heart stimulus pulses relative to the level of activity sensed.
2. Description of the related art including information disclosed under 37 CFR .sctn..sctn. 1.97-1.99.
Heretofore, various activity sensing pacemakers have been proposed. Examples of these previously proposed activity sensing pacemakers are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 4,140,132 Dahl 4,428,378 Anderson et al. 4,771,780 Sholder 4,846,195 Alt 4,860,751 Callaghan 4,869,251 Lekholm et al. 4,896,068 Nilsson 4,913,145 Stotts 4,940,052 Mann et al. 4,940,053 Mann et al. 5,010,893 Sholder ______________________________________
The Dahl U.S. Pat. No. 4,140,132 discloses a variable rate timer for a cardiac pacemaker including a piezoelectric element, a rectifier for rectifying the signals generated by the piezoelectric element and a capacitor network which receives the rectified pulses from the rectifier and stores those pulses therein. The stored pulses are supplied to the gate of a field effect transistor where a level or charge of voltage stored controls the current to the transistor which is used to control the pacing or timing rate of the pacemaker.
The activity sensing pacemaker of the present invention differs from the Dahl patent by sensing activity or motion along several different axes, preferably three axes, and does not rectify voltage generated by a piezoelectric element and does not have a voltage circuit including a constant timing resistor or a timing capacitor.
The Anderson U.S. Pat. No. 4,428,378 teaches a motion sensor that supplies signals to a level detector and band pass amplifier so that pulses above a certain level and within a certain frequency band only, are integrated to provide a control signal for controlling pacing.
The Sholder U.S. Pat. No. 4,771,780 teaches an activity sensor comprising a moving conducting element within a housing, as does the Lekholm et al. U.S. Pat. No. 4,869,251. In Lekholm et al. there is provided a hollow member with a freely movable member therein, the freely movable member generating a mechanical vibration upon movement by a patient. A transducer senses the vibration and generates an electrical signal corresponding to the mechanical vibrations. The electrical signal is proportionate to the movement and is used to vary the stimulation rate. In Sholder the moving conducting element within the cylindrical housing makes and breaks electrical contacts between at least two of a plurality of electrodes in the housing, the making and breaking of contacts being indicative of motion or activity of the patient.
The Alt U.S. Pat. No. 4,846,195 discloses an implantable position and motion sensor which includes a housing having a circular disc-like wall of electrically insulative material with conductive pins extending therethrough, a lid portion over the circular disc-like wall and a mercury ball within the housing and movable between the pins for effecting conduction between the pins. Movement of the mercury ball between the pins and the lid portion will generate signals indicating activity or movement of the patient and the position of the mercury ball indicates whether the patient is standing or lying down.
The Callaghan U.S. Pat. No. 4,860,751 teaches a passive activity sensor for a pacemaker requiring no power for sensing physical activity and a physical activity threshold detector.
The Nilsson U.S. Pat. No. 4,896,068 teaches the construction of an activity sensor having two individual or inter-related piezoceramic parts arranged side by side which are oppositely polarized and which are secured to a flat wall of a pacemaker housing.
The Stotts U.S. Pat. No. 4,913,145 discloses a cardiac pacemaker which has a sense amplifier for passing signal components lying in a selectively variable pass band.
The Alt U.S. Pat. No. 4,926,863 teaches the use of an accelerometer in a rate responsive cardiac pacemaker for sensing body movement and then selects only a portion of the electrical signal generated by the accelerometer at a frequency rate below 4 Hz to discriminate against signal components arising from other than physical exercise of the patient.
The Mann et al. U.S. Pat. No. 4,940,052 discloses a processor in a pacemaker which converts a raw signal generated by an activity sensor (a piezoelectric sensor) to a sensor-indicator rate signal in accordance with a selectable transfer relationship which defines the sensor-indicator rate signals as a function of a set of discrete sensor level index signals. The selected sensor level index signals is related to the energy content of the raw signal. Then, the selective sensor level index signal is used to control the pacing rate from a pulse generator.
The Mann et al. U.S. Pat. No. 4,940,053 discloses a rate responsive pacemaker having a piezoelectric sensor and a raw signal energy converter which amplifies the raw signal, rectifies the raw signal and then integrates the area of the raw signal in one embodiment of the energy converter.
In another embodiment of the energy converter, the durations of each rectified pulse of the raw signals are counted, individual duration counts are summed over a period of time (integrated) and the sum is utilized as an indication of the energy content of the raw signal. The level of the energy content is used to control the pacing rate of a pacemaker.
The Sholder U.S. Pat. No. 5,010,893 discloses a motion sensor mounted in a pacemaker. The motion sensor includes an enclosed housing having a movable conductive element therein that partially fills the space in the housing and is free to flow or otherwise move around the inside of the housing in response to external forces. As the conductive element moves within the enclosed housing, it makes electrical contact with at least two of three electrodes that are selectively spaced around the periphery of the housing in a manner similar to the movement of a contact in the earlier Sholder patent and the mercury ball in the earlier Alt patent.